A typical computer includes a clock generator that provides accurately timed pulses for synchronization. Some clock generators work off of a crystal, i.e., a natural or synthetic piezoelectric or semiconductor material which controls the frequency of oscillation of the clock signal. For example, some computers include a crystal driven clock generator that provides a system clock, i.e., a global clock signal which guides computer operations.
Clock generators are susceptible to failure. For example, a clock generator may stop providing pulses. Such a failure can be caused by an extreme operating environment (e.g., an excessive heat or humidity condition). Such a failure could also be caused by other factors such as gradual aging of the clock generator components (e.g., the crystal), poor quality components, or a manufacturing defect, etc.
Some computers include a clock detection circuit that monitors the operation of the clock generator. Such a circuit typically provides an error signal when it no longer detects the presence of a clock signal, i.e., when it no longer detects clock pulses from the clock generator. One example of a computer system, which uses such a detection circuit to detect the presence (or subsequent loss) of a system clock, is a conventional data communications device which sends and receives packets of data within a computer network.